Microelectromechanical Systems (MEMS) devices are typically attached to a housing structure, and the housing structure attached to another entity, such as a circuit board. External forces transmitted from the housing structure to the MEMS device may detrimentally affect the performance of the MEMS sensor or transducer located within the MEMS device. For example, if the sensor 30 comprises a bulk acoustic wave resonator having a disc shaped resonator element, such as disclosed in United States Patent Application Publication 2012/0227,487, the transducer may be supported at the disc center by an anchor. For other devices utilizing a capacitive resonator element, such as those disclosed in U.S. Pat. No. 7,023,065, an anchor may still support the transducer symmetrically so as not to bias the performance of the transducer due to its location.
While certain prior publications address how to protect MEMS devices with sensing gaps on the order of micrometers, they have not disclosed how to protect MEMS devices wherein the sensing gaps are on the order of nanometers. The susceptibility to interfering stimuli for devices based on nanometer distances for the sense gaps is perhaps 100 to 1000 times greater than those based on micrometer distances.
Devices with nanometer sized gaps are ˜100-1000 times more susceptible to induced strains caused by stresses, vibrations, thermal fluctuations than those with micrometer sized gaps. This is due to the fact that the minute fluctuations in gap distance caused by the stresses, vibrations and thermal transients are much larger fraction of the gap on a nanometer gapped device than a micrometer gapped device. This stems from the physics of how capacitance is defined. The change in gap causes a change in capacitance which causes a change in the output signal. When this gap distance is affected by stimuli other than the desired signal source, it is perceived as “noise” and is consequently undesirable.
There have been many disclosures relating to MEMS gyroscopes being fabricated on silicon die. While these disclosures have generally disclosed how to protect MEMS devices wherein the sensing gaps are on the order of micrometers; they have not disclosed how to protect MEMS devices wherein the sensing gaps are on the order of nanometers. The susceptibility to interfering stimuli for devices based on nanometer distances for the sense gaps is perhaps 100 to 1000 times greater than those based on micrometer distances. Some practices, in the past have involved using compliant adhesives, flexible substrates and mechanical flexures to address the issue of susceptibility. Devices with Nanometer sized gaps are ˜100-1000 times more susceptible to induced strains caused by stresses, vibrations, thermal fluctuations than those with micrometer sized gaps. This is due to the fact that the minute fluctuations in gap distance caused by the stresses, vibrations and thermal transients are much larger fraction of the gap on a nanometer gapped device than a micrometer gapped device. This stems from the physics of how capacitance is defined. The change in gap causes a change in capacitance which causes a change in the output signal. When this gap distance is affected by stimuli other than the desired signal source, it is perceived as “noise” and is consequently undesirable.
Accordingly, a need exists for a mechanism that isolates the transducer within a MEMS device from both internal and external stimuli.